1. Field of the Invention
The present invention generally relates to methods and apparatuses for processing an image signal and computer-readable recording media recorded with a program for causing a computer to process an image signal, and more particularly to a method and an apparatus for processing an image signal and a computer-readable recording medium recorded with a program for causing a computer to process an image signal, which relate an input image to a type of a drawing object in order to output an image of high quality.
2. Description of the Related Art
In a conventional image processing method, image data is input from a scanner or a host computer; output color elements C (Cyan), M (Magenta), Y (Yellow) and K (blacK), which are control signals of an image forming apparatus such as a color copier or the like, are processed by a uniform color conversion; and then the image data is output from the image forming apparatus such as the color copier or the like. In this conventional method, it is difficult to reproduce an optimized color of a compound document which document is displayed on a monitor of the host computer.
For example, different types of objects are combined by a page description language so that a compound document including both a monochrome photograph and a color photograph, a graphic image and text can be created. However, when the color conversion is conducted on the compound document based on a picture output, a text or a graphic image becomes a pale color with less impact. On the other hand, when a color of the compound document is reproduced with a strong saturation corresponding to a business graphic, a photograph color is deteriorated and a color selected as a background color is reproduced at high density. Consequently, characters on the background color are not clearly visible or easily readable.
Methods that solve the above problems are described, for example, in the Japanese priority applications No. 9-282471 and No. 9-193477.
In the Japanese priority application No. 9-282471, based on an image type (character data, graphic data or raster graphic data) in the page description language, a characteristic of each pixel is determined. Also, technologies for conducting processes, which influence a print quality, such as a middle tone process, a gamma correction, a filter process and a masking process, are described. Thus, according to the invention described in the Japanese priority application No. 9-282471, it is possible to control an image output signal based on the image type and to output an image of high-grade quality.
In addition, in the Japanese priority application No. 9-193477, a color printer is described in which print data is referred to, an attribute related to color correction for each object is determined and a color correction function corresponding to the determined attribute is selected. Thus, according to the invention described in the Japanese priority application No. 9-193477, each object type is automatically determined and the color correction is conducted for each object.
The color correction in the invention in the Japanese priority application No. 9-193477 will be now described.
In general, a color reproduction range of an electronic picture or inkjet printer is narrower than that of a television set, a CRT display or the like. Thus, various color correction technologies have been proposed for correcting a difference between the color reproduction range of an input color image and that of an output color image. The color correction technologies are always required for a color image output apparatus if it has a limited the color reproduction range.
Regarding the color correction, further methods that solve the above problems are described, for example, in the Japanese priority applications No. 4040072 and No. 7-327141.
In a color correction method described in the Japanese priority application No. 4040072, it is determined whether or not a desired color in a uniform color space or an HVC color space (a color space consisted of information of brightness, hue and saturation) is out of the color reproduction rage for an output image. That is, when the desired color is out of the color reproduction rage for an output image, a saturation having the same brightness and hue as the desired color is corrected to be a maximum value and then the image is output.
Moreover, in a color image signal processing method described in the Japanese priority application No. 7-327141, a brightness component is compressed in accordance with a reproduction brightness ratio of an input system to an output system and then a saturation component is compressed and converted into color image data within the color reproduction range of the output image.
However, in the inventions described in the Japanese priority applications No. 9-282471 and No. 9-193477, the image output signal is controlled by the image type alone. That is, an object color is controlled regardless of a background color. Thus, an unbalance between the object color and the background color still remains.
Consequently, the above inventions have a disadvantage in that characters on the background color are not clearly visible and easily readable.
Also, according to the inventions described in the Japanese priority applications No. 4040072 and No. 7-32714, the color correction is controlled regardless of the background color. Thus, the color correction is not properly conducted relative to the background color.
Consequently, these inventions have a disadvantage in that characters on the background color are not clearly visible and easily readable.